Hi, I was trying to understand how the transfer function is derived from a sallen-key topology using this pdf on page 2: http://www.vyssotski.ch/BasicsOfInstrumentation/AnalysisOfTheSallen-KeyArchitecture.pdf

He starts by using kirchoffs law to obtain equations at certain points. What i was wondering is, at equation 1, how does the author conclude to such results when kirchoffs law states that at a node, all the currents are equal to zero.

Thanks

 

Never mind. he is actually taking them equal to zero. sorry for the stupid question

 

Look at those two figures.

The first diagram shows I Kirchhoff's law.




Current entering the node must be equal the current that is leaving the node.

And this diagram shows II Kirchhoff Law

 

nice pictures...